Coordinate measuring machines

The purpose of this study was to investigate the validity of linear position
transducers (LPTs), The Open Barbell System (OBS) and Tendo Weightlifting Analyzer
System (TWAS), in comparison to criterion measure Optotrak Certus (OC3D). Further,
we aimed to compare LPTs against each other. Twenty-five resistance-trained males were
recruited, and reported to the laboratory for one day of data collection. Subjects
performed one-repetition maximum (1 RM) testing of the squat, then had a standardized
rest before completing one set to failure with 70% 1 RM. There was no significant
difference in average velocity (AV) between either LPT vs. OC3D. T-tests revealed
significant differences between LPTs and OC3D peak velocity (PV) (OBS: p=0.02080;
TWAS: p<0.01). A significant difference was detected between OBS and TWAS PV
(p<0.01). OBS and TWAS demonstrated concurrent validity compared to OC3D for AV
(OBS: p=0.2014; TWAS: p=0.5466). Neither LPT was a valid measure ofPV (OBS:
p=0.0208; TWAS: p<0.01).

To assess and improve the accuracy of an intelligent machine such as a precision robot and a computer numerically controlled machine tool, it is exceedingly desirable to have a high performance Coordinate Measuring Machine (CMM). Among various coordinate measuring devices, a laser tracking CMM has the advantages of noninvasiveness and extremely high precision over a large workspace. In this dissertation, we concentrate on the design and control of a new type of spherical gimbal for laser tracking system, whose motion is constrained by two spherical surfaces and whose axes are motorized. By this design, principal errors of a conventional tracking gimbal are reduced. To be able to integrate the laser tracking unit into an intelligent machine, a compact optical head is also designed. This laser tracking system is thus capable of being either a stand-alone or an on-line measuring device. An important issue in developing a laser tracking CMM is control. An intelligent control scheme is reported in this dissertation. The controller has the following elements: The entire tracking process of the system is classified into three modes: normal tracking, motionless and change of directions. An artificial neural network is designed to classify on-line which mode the system is in. A Fuzzy Logic Controller (FLC) suitable for the particular tracking mode is then activated to control the system. To deal with the situation in which a target suddenly changes its direction, a feed-forward compensation component is designed. Decoupling units are also added to the control scheme, by which the entire process of tracking controller design can be greatly simplified. To further improve the system performance, various structures of FLCs are analyzed in the dissertation. It is discovered that there is a constraint in the cascade proportional-integral-derivative (PID)-type FLC. Whenever this constraint is violated, the design of the controller will not be optimal. To solve this problem, a parallel PID-type FLC is proposed. Yet another important issue in the system control is parameter tuning. To this end, a mu-law tuning method, which tune both scaling gain and surface of a fuzzy look-up table, is proposed. A new parameter tuning strategy, which combines mu-law with either a Genetic Algorithm (GA) or a downhill simplex algorithm, is introduced. The GA based mu-law tuning of FLCs can automatically tune parameters of the FLCs, while the Simplex-mu-law tuning scheme can reach near optimal results rapidly. To assess the effectiveness of the concepts proposed in this dissertation, a prototype spherical laser tracking gimbal is constructed at the FAU Robotics Center. The control strategy proposed in this dissertation is tested extensively by simulation and experimentation on the prototype system.